Translations:Rust installation special notes in China/7/en

RUSTUP_UPDATE_ROOT=https://mirrors.sjtug.sjtu.edu.cn/rust-static/rustup RUSTUP_DIST_SERVER=https://mirrors.sjtug.sjtu.edu.cn/rust-static [source.crates-io] replace-with = 'sjtu'
 * SJTUG mirror (https://mirrors.sjtug.sjtu.edu.cn/)